Code division multiple access (CDMA) networks allow a number of communication signals to operate over the same frequency band simultaneously. Each communication unit is assigned a distinct, pseudo-random, chip code which identifies signals associated with the communication unit. The communication units use this chip code to pseudo-randomly spread their transmitted signal over the allotted frequency band. Accordingly, signals may be communicated from each such unit over the same frequency band and a receiver may despread a desired signal associated with a particular communication unit.
However, despreading of the desired communication unit's signal results in the receiver not only receiving the energy of this desired signal, but also a portion of the energies of other communication units operating over the same frequency band. Accordingly, CDMA networks are interference limited, i.e., the number of communication units using the same frequency band, while maintaining an acceptable signal quality, is determined by the total energy level within the frequency band at the receiver.
In order to provide reasonable capacity in the CDMA network, the mobile units are typically power controlled to reduce energy transmitted within the CDMA frequency band while maintaining sufficient power to provide an acceptable signal at a receiving unit. Through intelligent power control, the signals from all of the communication units may be adjusted to arrive at a receiver with substantially the same signal to interference ratio. As such, no one communication unit's signal will contribute excess energy to the total energy within the frequency band at the receiver.
Accordingly, in a cellular communication network, a base transceiver station (BTS), base station controller (BSC), or the like, may operate to control the power of mobile units such that each unit's signal, regardless of its location within a cell, is received at the BTS with the same signal to interference ratio. However, if a particular mobile, such as a rogue or malfunctioning mobile, is under power control but fails to operate in the required fashion, i.e., fails to respond properly to the power control commands sent to it, then it is likely that excess energy will be experienced at the BTS. Accordingly, this rogue mobile's signal will cause extra interference to other mobiles in the cell and, effectively, reduce the capacity of a particular cell or sector.
Moreover, as cellular CDMA networks typically utilize the same frequency band throughout neighboring cells, relying on different chip codes to identify particular mobiles assigned to each cell, the energy at any BTS is also affected by mobile units operating in neighboring cells. Therefore, a particular neighboring cell which is heavily loaded, i.e., providing communications for a large number of mobile units, may cause increased interference at the BTS. Similarly, a rogue mobile, as discussed above, even though operating in a neighboring cell may cause the above described interference at the BTS.
Additionally, it is also possible, in a CDMA network, for jamming interference or external interference to affect a particular cell or sector in such a way as to dramatically reduce the capacity. For example, any energy within the CDMA frequency band, whether sourced from in the network elements or externally, may increase the energy level at a particular BTS.
Accordingly, a need exists in the art for a system and method for mitigating the effects of undesired energy at a CDMA receiver site.
A further need exists in the art for the system and method mitigating the effects of undesired energy to not unnecessarily affect energy levels of desired signals within the frequency band.